The invention relates to nanopositioners. In particular, the invention relates to novel materials for making nanopositioners.
Complete bibliographic citations to the references discussed herein are contained in the Bibliography section, directly preceding the claims.
It is common knowledge that electronic devices continue to grow more powerful and more versatile at the same time as they continue to become physically smaller. Only a few years ago, line widths of the order of 0.5 xcexcm were available from only the most advanced semiconductor manufacturers. Today, manufacturers routinely use 0.25 xcexcm design-rules, with 0.18 1 xcexcm beginning to come into play. Smaller feature sizes are on the horizon, providing the driving force for the development of next generation lithography techniques such as SCALPEL(copyright) (SCattering with Angular Limitation Projection Electron-beam Lithography) and Extreme Ultraviolet (EUV) photolithography.
With these changes comes a pressing need to inspect the wafers produced rigorously, and even to inspect some of the tools used to produce the wafers, such as advanced photomasks. With the smaller features it creates, next generation lithography demands use of critical dimension (CD) surface metrology that is faster and more accurate than ever. Providing CD metrology in turn requires the ability to move a probe across a surface to be inspected in the X and Y directions, and to be able to move the probe toward and away from that surface in the Z direction rapidly, repeatedly, precisely, and accurately.
Nanopositioners based upon flexure hinge designs provide this type of precise, fine-scale motion in X, XY, or XYZ directions. Nanopositioners also have been developed for use in precision machining, optical switching, cell physiology research, and other applications. The material currently used in fabricating the vast majority of such nanopositioners is Al 7075 alloy. Other aluminium alloys may be used in instances requiring compatibility with an ultra-high vacuum or non-magnetic service environment. Nanopositioners requiring extreme positioning precision (at the expense of speed) may be made from materials having a relatively low coefficient of thermal expansion (CTE), such as invar alloys. Nanopositioners made from the current materials provide only modest performance, where they can be used at all. Some further limited improvement in nanopositioner performance might be obtained with these materials using new designs for the flexure hinges and for the electronics driving the nanopositioner, especially in positioning feedback circuitry.
Significant changes in nanopositioner performance, however, will require changes in flexure design, and corresponding changes in driver design, that cannot be supported with current materials. In particular, the range of motion of nanopositioners utilizing flexure stages is not expected to exceed perhaps 300 micrometers using current materials; such nanopositioners in addition will require a physical size (footprint) inappropriately large for many applications. New materials having greater specific stiffness and flexural strength are the key to developing next-generation nanopositioners. Such new materials and linear flexure motion nanopositioners fabricated therefrom are described herein.
The invention, which is defined by the claims set out at the end of this specification, is intended to solve at least some of the problems noted above. A nanopositioner is provided that is fabricated from a ceramic matrix composite having a matrix material and a reinforcing phase. A preferred embodiment of the matrix material is a cermet, and more preferably is an aluminum boron-carbide or MoSi2.
A preferred embodiment of the ceramic matrix composite is a graphite/epoxy composite, such as a graphite whisker/epoxy composite.
Another preferred embodiment of the ceramic matrix composite is a two-dimensional C/C composite. Preferably, the two-dimensional C/C composite is chemically converted to C/SiC or SiC/SiC after it is machined.
The ceramic matrix composite preferably has sufficient electrical conductivity to support wire electric discharge machining. This property supports the introduction of a flexure hinge pattern into a stage blank by wire electric discharge machining.
Also preferred is a ceramic matrix composite having a natural frequency for the first vibrational mode that is at least twice that of Al 7075 and having an out-of-plane motion that is a fraction of that experienced with Al 7075 for an identical stage design.
The reinforcing phase of the ceramic matrix composite preferably is an electrically conductive material, such as graphite whiskers or graphite fiber.
Further advantages, features, and objects of the invention will be apparent from the following detailed description of the invention in conjunction with the associated drawings.